GMCforum: GMCnet » Fuel gauge not working, need help

Home » Public Forums » GMCnet » Fuel gauge not working, need help

Show: Today's Messages :: Polls :: Message Navigator

Fuel gauge not working, need help [message #225531]

Sun, 13 October 2013 20:36

lw8000

Messages: 201
Registered: July 2012
Location: S.E. Michigan

Karma: 1

Senior Member

Hello all,

We are having a difficult time trying to fix the fuel gauge on our 77 Kingsley, and need some help and advice. The problem we are facing is the fuel gauge stays on E pretty much all of the time, no matter which tank we have the switch set to (main or aux). Once in a while, the gauge will work but not for long.

After reading here about how to check the sending units, I removed the plug from the back of the fuel selector switch, and with the ignition key on checked and we have 90 ohms from one sending unit, and 25 ohms from the other sending unit. I also tested the switch itself, and it is working properly. Next, I checked continuity of two wires (one is pink and one is gray) that go from the switch to the plug on the back of the gauge itself, and they show as good. Next, I tried to check resistance of those same two wires on the gauge plug, and seemed to get a zero reading on both wires. This is where I'm stumped. I am certain that both sending units and the switch are fine, but I'm assuming that I should be able to check resistance at that plug. Is this assumption correct? Is there a better way to check the connection at the gauge or check the gauge itself?

We have also checked that the ground that connects to the back of the gauges is good.

Any help would be greatly appreciated!!! We are close and it will be nice knowing how much fuel we have in the tanks... Smile

Thank you !
--
Chris

Chris S. - 77 Kingsley, 3.70 FD, mostly OEM - S.E. Michigan

[Updated on: Sun, 13 October 2013 20:41]

Report message to a moderator

Re: Fuel gauge not working, need help [message #225539 is a reply to message #225531]

Sun, 13 October 2013 21:13

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

Karma: 7

Senior Member

lw8000 wrote on Sun, 13 October 2013 21:36

Thank you !
--
Chris

Chris,

With the coach sending units: 90 ohms is full.
The 25 ohm would be about 1/3, but you can't do that with one tank full. The way the system is plumbed, it just can't happen.

Is the one gage really 90 ohms?
Or is it just railed out on your meter?
Did you disconnect the sending unit leads on the switch?
You do have to do that for this test or at least test the unused sender (and since I can never get that straight, I pulled both wires).

The ignition on or off should make no difference if they sending units are disconnected. If you have the sending units disconnected and the instrument still reports empty, then the instrument is bad. It should go to full+ with the sending unit disconnected and the ignition on.

You have no geographic reference anywhere, so I won't invite you to call me so I can walk you though this. If you are eastern or even central, that is possible. I have been around this block and don't mind sharing hard won lessons at reasonable hours of the day.

Matt

Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

Report message to a moderator

Re: Fuel gauge not working, need help [message #225571 is a reply to message #225539]

Mon, 14 October 2013 07:55

lw8000

Messages: 201
Registered: July 2012
Location: S.E. Michigan

Karma: 1

Senior Member

Matt Colie wrote on Sun, 13 October 2013 21:13

With the coach sending units: 90 ohms is full.
The 25 ohm would be about 1/3, but you can't do that with one tank full. The way the system is plumbed, it just can't happen.

Is the one gage really 90 ohms?
Or is it just railed out on your meter?
Did you disconnect the sending unit leads on the switch?
You do have to do that for this test or at least test the unused sender (and since I can never get that straight, I pulled both wires).

The ignition on or off should make no difference if they sending units are disconnected. If you have the sending units disconnected and the instrument still reports empty, then the instrument is bad. It should go to full+ with the sending unit disconnected and the ignition on.

You have no geographic reference anywhere, so I won't invite you to call me so I can walk you though this. If you are eastern or even central, that is possible. I have been around this block and don't mind sharing hard won lessons at reasonable hours of the day.

Matt

Hi Matt,

Thanks for your help on this. We did top the coach off recently, so I was also expecting both sending units to show around 90 ohms. Right now I do know the back is sitting lower than the front at the time of testing, but I don't see why it would only read 25 ohms. Unfortunately I did not pay enough attention to which sender read 90 and which 25. As far as I know, my multimeter is OK (I hope!!).

We did the resistance test by disconnecting the plug from the back of the fuel selector switch, yes. I then tested the resistance on the two leads on that plug, that come from both sending units, with it disconnected.

We will check the gauge today and see if it reads empty. I'm guessing that by simply pulling the plug from the back of the fuel selector switch, this will be good enough to check the gauge (assuming it should read full at that point since there would be no signal coming from the sending units)?

I am actually located not too far from you, between Lansing and Detroit. I will try to update my profile soon , as I can see that would be helpful.

Thanks again.... will post back any further results.

--
Chris

Chris S. - 77 Kingsley, 3.70 FD, mostly OEM - S.E. Michigan

Report message to a moderator

Re: Fuel gauge not working, need help [message #225574 is a reply to message #225531]

Mon, 14 October 2013 08:36

RF_Burns

Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada

Karma: 3

Senior Member

Assuming the gauge works and has power, showing Empty means the wire to the sensor is pulled to ground (zero ohms at the sensor)

Pull the connector off the back of the fuel switch and see if it goes to Full. If so, look for shorted (pinched) wires going to the back sensors. If it doesn't change then I would suspect a power issue or a gauge issue.

I don't know the circuitry inside the low fuel warning module so it also could be faulty, pull it from the harness and see if that fixes it.

The above is going from memory of the fuel gauge circuit, so I could be completely wrong!

Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

Report message to a moderator

Re: Fuel gauge not working, need help [message #225575 is a reply to message #225571]

Mon, 14 October 2013 08:49

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

Karma: 7

Senior Member

lw8000 wrote on Mon, 14 October 2013 08:55

OK Chris,

You have most of this right. Great!

If you want to check the gage, get a clip lead and ground one of the senders. That will do no harm and should send the gage needle to empty.

What I really can't figure out is the 25 ohm reading. That one just makes no sense at all. Are you sure you are on the other sender and not the selector valve? As the senders age and are slowly destroyed by the alcohol, the resistance move higher. It they get real bad they either go open (full+) but I did see one short to ground.

Now that I know you are only about an hour away, and even in the same time zone, call me if you need someone to bounce thoughts off. My cell is 73four - 55two - 35two3 and if we need to talk longer, I will call you back as my home phone only bills by the month. I can also be there in about an hour with instruments and some hard won experience.

It is real nice to have fuel gages that more or less work.

Matt

Report message to a moderator

Re: Fuel gauge not working, need help [message #225735 is a reply to message #225531]

Tue, 15 October 2013 12:44

lw8000

Messages: 201
Registered: July 2012
Location: S.E. Michigan

Karma: 1

Senior Member

Thank you for all of the replies and information.

We think we finally found the culprit of our issues, which seems to be bad wiring in the dash. We found a spot where the wires have a sharp bend in them and after unbending slightly, the fuel gauge is now working. Incidentally, it is a gray colored wire that sends the signal from the fuel selector switch (when looking at the switch, the gray wire connects to the middle pin toward the driver's side), to the fuel gauge. That was the wire at fault here.

Why the one sender unit is at 25 ohms (when the tank is close to full), is still a mystery to us. However we will get by as-is for now.

Thank you Matt for your help and for your generous offer to discuss this and even come up to help. We've learned a lot and are still learning more ever day with everybody's help. Hopefully this discussion will also help others with similar issues, too.

--
Chris

Chris S. - 77 Kingsley, 3.70 FD, mostly OEM - S.E. Michigan

[Updated on: Tue, 15 October 2013 12:45]

Report message to a moderator

Re: [GMCnet] Fuel gauge not working, need help [message #225736 is a reply to message #225735]

Tue, 15 October 2013 13:15

sgltrac

Messages: 2797
Registered: April 2011

Karma: 1

Senior Member

Where u from Chris and what coach you got? (Fill out a sig line in the birdfeeder). It helps everyone no where u @ and what coach.

Todd Sullivan

Sully
77 royale
Seattle

> On Oct 15, 2013, at 10:44 AM, LW <tux@apex-internet.com> wrote:
>
>
>
> Thank you for all of the replies and information.
>
> We think we finally found the culprit of our issues, which seems to be bad wiring in the dash. We found a spot where the wires have a sharp bend in them and after unbending slightly, the fuel gauge is now working. Incidentally, it is a gray colored wire that sends the signal from the fuel selector switch (when looking at the switch, the gray wire connects to the middle pin toward the driver's side), to the fuel gauge. That was the wire at fault here.
>
> Thank you Matt for your help and for your generous offer to discuss this and even come up to help. We've learned a lot and are still learning more ever day with everybody's help. Hopefully this discussion will also help others with similar issues, too.
>
> --
> Chris
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

Sully 77 Royale basket case. Future motorhome land speed record holder(bucket list) Seattle, Wa.

Report message to a moderator

Re: Fuel gauge not working, need help [message #225737 is a reply to message #225575]

Tue, 15 October 2013 13:57

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

Matt Colie wrote on Mon, 14 October 2013 08:49

...What I really can't figure out is the 25 ohm reading. ...

The float is stuck.

Report message to a moderator

Re: Fuel gauge not working, need help [message #225752 is a reply to message #225531]

Tue, 15 October 2013 15:34

mickey szilagyi

Messages: 273
Registered: January 2013

Karma: 0

Senior Member

That's a pretty good possibility, stuck float. We just had the tanks renued and the sending units checked. We never were able to see this particular one in operation as our fuel gage didn't work. And we didn't check the Ohms reading on them prior to a few days ago. The service people however never commented on the sending unit getting stuck but who knows sometimes service people have their heads somewhere besides on their task at hand.

We're going to be using the coach soon hopefully on a couple hundred mile trip so the sending units should get some exercise. Either it will stay put or break loose if it's stuck.

Thanks for the suggestion.

Same coach as Chris, I'm his dad.

Mickey 1977 Kingsley, 403, Lansing, MI

Report message to a moderator

Previous Topic:	[GMCnet] Harbor Freight Chair
Next Topic:	[GMCnet] 6K onan muffler fixed

Goto Forum:

-=] Back to Top [=-

Current Time: Thu Sep 19 18:03:49 CDT 2024

Total time taken to generate the page: 0.01610 seconds